AKS-74U
In 1979, a shortened carbine variant of the AKS-74 was adopted into service with the Soviet Army: the AKS-74U (U—''Ukorochenniy'', lit. Shortened), which in terms of tactical deployment, bridges the gap between a submachine gun and an assault rifle. It was intended for use mainly with special forces, airborne infantry, rear-echelon support units and armored vehicle crews. It is still used in these roles, but has been augmented by various submachine guns, and the AK-105. It is also commonly used by law enforcement; for example, each urban police foot patrol is issued at least one. The rifle's compact dimensions, compared to the AKS-74, were achieved by using a short 210 mm (8.3 in) barrel (this forced designers to simultaneously reduce the gas piston operating rod to an appropriate length). In order to effectively stabilize projectiles, the barrel’s twist rate was increased from 200 mm (1:8 in) to 160 mm (1:6.3 in). A new gas block was installed at the muzzle end of the barrel with a new conical flash hider combined with a cylindrical muzzle booster, which features an internal expansion chamber that increases the weapon's reliability. The booster supplies an increased amount of residual gas from the barrel for the gas system. The chrome-lined muzzle booster also burns any remaining propellant thus reducing the gun's signature. The muzzle device locks into the gas block with a spring-loaded detent and features two notches cut into the flash hider cone, used for disassembly using the supplied cleaning rod. The forward sling loop was relocated to the left side of the carbine and the front sight was integrated into the gas block. The AKS-74U also has a different sighting system with a U-shaped flip sight instead of the standard sliding notch rear sight. This sight has two settings: "P" (calibrated for firing at 350 m) and "4–5" (used for firing at distances between 400–500 m). The rear sight is housed in a semi-shrouded protective enclosure that is riveted to the receiver's top cover. This top cover is integral with the gas tube cover and hinged from the barrel trunnion, pivoting forward when opened. Both the gas tube and handguard are also of a new type and are shorter than the analogous parts in the AKS-74. The AKS-74U is significantly more maneuverable in tight quarters than the AKS-74; however, the significant decline in muzzle velocity from 900 m/s (2,952.8 ft/s) to 735 m/s (2,411.4 ft/s) resulted in a decrease in effective range (the effective hitting distance for a "running"-type silhouette target was reduced from 625 to 350 m). The carbine cannot mount a bayonet or standard under-barrel grenade launcher. However, a suppressed 30 mm BS-1 grenade launcher was developed specifically for that platform that fires a high-explosive dual purpose (HEDP) grenade. The grenades for the BS-1 are launched by blank cartridges and the rifle is cycled manually in this mode of operation. The majority of AKS-74U carbines were manufactured at the Tula Arms Factory rather than Izhmash. The AKS-74U was also used as the basis for several other unique weapons, including the bullpup OTs-14 Groza specialist carbine and the Gepard series of multi-caliber submachine guns (none of which evolved past prototype stage). Trivia *Most people commonly refer to this weapon as AK-74U